Method and Structure for FinFET Device

ABSTRACT

The present disclosure provides a method, which includes forming a first fin structure and a second fin structure over a substrate, which has a first trench positioned between the first and second fin structures. The method also includes forming a first dielectric layer within the first trench, recessing the first dielectric layer to expose a portion of the first fin structure, forming a first capping layer over the exposed portion of the first fin structure and the recessed first dielectric layer in the first trench, forming a second dielectric layer over the first capping layer in the first trench while the first capping layer covers the exposed portion of the first fin feature and removing the first capping layer from the first fin structure.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. In the course of IC evolution,functional density (i.e., the number of interconnected devices per chiparea) has generally increased while geometry size (i.e., the smallestcomponent (or line) that can be created using a fabrication process) hasdecreased. This scaling down process generally provides benefits byincreasing production efficiency and lowering associated costs.

Such scaling down has also increased the complexity of processing andmanufacturing ICs and, for these advances to be realized, similardevelopments in IC processing and manufacturing are needed. For example,a three dimensional transistor, such as a fin-like field-effecttransistor (FinFET), has been introduced to replace a planar transistor.Furthermore, epitaxy growth, such as silicon germanium, is alsointroduced to transistors. Although existing FinFET devices and methodsof fabricating FinFET devices have been generally adequate for theirintended purposes, they have not been entirely satisfactory in allrespects. For example, challenges rise to avoid adverse impacts on finstructure during the formation of isolation regions.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a flow chart of an example method for fabricating asemiconductor device in accordance with some embodiments.

FIGS. 2A, 2B, 3A, 3B, 4A, 4B, 5A, 5B, 6A, 6B, 7A, 7B, 8A, 8B, 9A, 9B,10A, 10B, 11A, 11B, 12A, 12B, 13 a, 13B, 14A, 14B, 15A, 15B, 16A, 16B,17A, 17B, 18A, 18B, 19A and 19B are diagrammatic perspective views of anexample semiconductor device undergoing processes in accordance withsome embodiments.

FIGS. 20A and 21A are cross-sectional views of an example device inaccordance with some embodiments, along the line A-A in FIG. 19A.

FIG. 20B is a cross-sectional views of an example device in accordancewith some embodiments, along the line A-A in FIG. 19B.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

The present disclosure is directed to, but not otherwise limited to, afin-like field-effect transistor (FinFET) device. The FinFET device, forexample, may be a complementary metal-oxide-semiconductor (CMOS) deviceincluding a P-type metal-oxide-semiconductor (PMOS) FinFET device and anN-type metal-oxide-semiconductor (NMOS) FinFET device. The followingdisclosure will continue with a FinFET example to illustrate variousembodiments of the present invention. It is understood, however, thatthe application should not be limited to a particular type of device,except as specifically claimed.

FIG. 1 is a flowchart of a method 100 for fabricating a semiconductordevice 200 according to aspects of the present disclosure. FIGS. 2Athrough 19B are side-perspective views of the semiconductor device 200manufactured according to the method 100. FIGS. 20A-21A arecross-section views of the semiconductor device 200 manufacturedaccording to the method 100. In FIGS. 2A through 21A, figures endingwith an “A” designation illustrate a first region of the semiconductordevice 200; figures ending with a “B” designation illustrate a secondregion. In the present embodiment, the first region is an NMOS regionand the second region is a PMOS region.

Referring to FIGS. 1 and 2A-2B, the method 100 begins at operation 102by providing a substrate 210. In the present embodiment, the substrate210 is a bulk silicon substrate. Alternatively, the substrate 210 mayinclude an elementary semiconductor, such as silicon or germanium in acrystalline structure; a compound semiconductor, such as silicongermanium, silicon carbide, gallium arsenic, gallium phosphide, indiumphosphide, indium arsenide, and/or indium antimonide; or combinationsthereof.

In another embodiment, the substrate 210 has a silicon-on-insulator(SOI) structure with an insulator layer in the substrate. An exemplaryinsulator layer may be a buried oxide layer (BOX). The SOI substrate maybe fabricated using separation by implantation of oxygen (SIMOX), waferbonding, and/or other suitable methods.

The substrate 210 may include integrated circuit devices (not shown). Asone of ordinary skill in the art will recognize, a wide variety ofintegrated circuit devices such as transistors, diodes, capacitors,resistors, the like, and/or combinations thereof may be formed in and/oron the substrate 210 to generate the structural and functionalrequirements of the design for the FinFET. The integrated circuitdevices may be formed using any suitable methods.

Referring again to FIGS. 1 and 2A-2B, the method 100 proceeds to step104 by forming a first patterned hard mask (HM) 212 to cover the PMOSregion while leaving the NMOS region uncovered. The first patterned HM212 may be formed by processes including depositing, patterning andetching. The first patterned HM 212 may include silicon oxide, siliconnitride, silicon oxynitride, or any other suitable dielectric material,formed by thermal oxidation, chemical vapor deposition (CVD), atomiclayer deposition (ALD), or any other appropriate method.

Referring to FIGS. 1 and 3A-3B, the method 100 proceeds to step 106 byforming a first semiconductor material layer 310 over the substrate 210in the NMOS region while the PMOS region is covered by the firstpatterned HM 212. In the present embodiment, the first semiconductormaterial layer 310 is deposited by an epitaxial growth. In variousexamples, the epitaxial processes include CVD deposition techniques(e.g., vapor-phase epitaxy (VPE) and/or ultra-high vacuum CVD(UHV-CVD)), molecular beam epitaxy, and/or other suitable processes. Thefirst semiconductor material layer 310 and the semiconductor material ofsubstrate 210 are different from each other. In the present embodiment,the first semiconductor material layer 310 includes silicon germanium(SiGe). In various examples, the first semiconductor material layer 310may include germanium (Ge), silicon (Si), gallium arsenide (GaAs),aluminum gallium arsenide (AlGaAs), silicon germanium (SiGe), galliumarsenide phosphide (GaAsP), or other suitable materials.

Referring to FIGS. 1 and 4A-4B, the method 100 proceeds to step 108 byforming a second semiconductor material layer 320 over the firstsemiconductor material layer 310 in the NMOS region and over thesubstrate 210 in the PMOS region. Prior to forming the secondsemiconductor material layer 320, the first patterned HM 212 is removedby an etching process, such as a selective wet etch. The first andsecond semiconductor material layers, 310 and 320, are different fromeach other. In the present embodiment, the first semiconductor materiallayer 310 includes SiGe while the second semiconductor material layer320 includes Si. In various examples, the second semiconductor materiallayer 320 may include Ge, GaAs, AlGaAs, SiGe, GaAsP, or other suitablematerials. The second semiconductor material layer 320 is formedsimilarly in many respects to the first semiconductor material layer 310discussed above in association with FIGS. 3A-3B.

Referring to FIGS. 1 and 5A-5B, the method 100 proceeds to step 110 byforming a blanket HM 330 over the second semiconductor material layer320 in both the NMOS region and the PMOS region. The blanket HM 330 mayinclude silicon nitride, silicon oxynitride, silicon carbide, siliconcarbon nitride, the like, or a combination thereof. In some embodiments,prior to depositing the blanket HM 330, a pad oxide layer 325 isdeposited over the second semiconductor material layer 320 first toprovide a stress buffer between the second semiconductor material layer320 and the blanket HM 330. The blanket HM 330, as well as the pad oxidelayer 325, may be formed by CVD, PVD, ALD, or other proper techniques.

Referring to FIGS. 1 and 6A-6B, the method 100 proceeds to step 112 byforming first fins 410 in the NMOS region and second fins 420 in thePMOS region, as well as fin trench 430 between first fins 410 and fintrench 440 between second fins 420. The first and second fins, 410 and420, are formed by etching the blanket HM 330 (as well as the pad oxidelayer 325 if present), the second and first semiconductor materiallayers, 320 and 310, and the substrate 210.

The etching process may include a wet etch, a dry etch, or a combinationthereof. In one embodiment, the wet etching solution includes atetramethylammonium hydroxide (TMAH), a HF/HNO₃/CH₃COOH solution, orother suitable solution. The respective etch process may be tuned withvarious etching parameters, such as etchant used, etching temperature,etching solution concentration, etching pressure, source power, RF biasvoltage, RF bias power, etchant flow rate, and/or other suitableparameters. For example, a wet etching solution may include NH₄OH, KOH(potassium hydroxide), HF (hydrofluoric acid), TMAH (tetramethylammoniumhydroxide), other suitable wet etching solutions, or combinationsthereof. In another embodiment, the dry etching processes include abiased plasma etching process that uses a chlorine-based chemistry.Other dry etchant gasses include CF₄, NF₃, SF₆, and He. Dry etching mayalso be performed anisotropically using such mechanism as DRIE (deepreactive-ion etching).

Alternatively, a patterned photoresist layer is formed over the blanketHM 330 and the blanket HM 330 is then etched through the patternedphotoresist layer to pattern the blanket HM 330. After patterning theblanket HM 330, the patterned photoresist layer is removed. And then thesecond and first semiconductor layers, 320 and 310, and the substrate210 are etched through the patterned HM 330.

In the present embodiment, the etching depth is controlled such that thefirst and second semiconductor layers, 310 and 320 are fully exposed inthe fin trench 430 adjacent first fins 410 and that the secondsemiconductor layer 320 is fully exposed in the fin trench 440 adjacentsecond fins 420.

Referring to FIGS. 1 and 7A-7B, the method 100 proceeds to step 114 byconverting the first semiconductor material layer 310 to a dielectriclayer 510 for device electric insulation enhancement. In someembodiments, the conversion process is an oxidation process. In oneembodiment, the thermal oxidation process is conducted in oxygenambient. In another embodiment, the thermal oxidation process isconducted in a combination of steam ambient and oxygen ambient. Duringthe thermal oxidation process, at least side portions of the firstsemiconductor material layer 310 converts to dielectric layer 510.

As an example, the first semiconductor material layer 310 includesSiGe_(x), here the subscript x is Ge composition in atomic percent. Thefirst semiconductor material layer 310 is partially or completelyoxidized by the thermal oxidation process, thereby forming semiconductoroxide layer 510 that includes silicon germanium oxide (SiGeO_(y)) orgermanium oxide (GeO_(y)), where subscript y is oxygen composition inatomic percent.

In some embodiments, during the thermal oxidation process, the exposedsecond semiconductor material layer 320, in both of the first and secondfins, 410 and 420, may also be partially oxidized to a semiconductoroxide layer 520 on the exposed surface thereof. In such a scenario, thethermal oxidation process is controlled such that the semiconductormaterial layer 320 oxidizes much slower than the first semiconductormaterial layers 310 does. As such, the second semiconductor oxide layer520 is thinner than the first semiconductor oxide layer 510.

For example, in some embodiments the thermal oxidation process isperformed in a H₂O reaction gas with a temperature ranging from about400° C. to about 600° C. and under a pressure ranging from about 1 atm.to about 20 atm. In some embodiment, after the oxidation process, thesemiconductor oxide layer 550 is removed by a cleaning process includingusing diluted hydrofluoric (DHF) acid. In some embodiment, thesemiconductor oxide layer 520 is not removed. For clarity, in subsequentdrawings, the semiconductor oxide layer 520 will not be illustrated asit has been removed by a cleaning process.

Referring to FIGS. 1 and 8A-8B, the method 100 proceeds to step 116 byfilling the fin trenches 430 and 440 with a first dielectric layer 530to separate first fins 310 from each other and separate second fins 320from each other. The first dielectric layer 530 may include siliconoxide, silicon nitride, silicon oxynitride, an air gap, other suitablematerials, or combinations thereof. The first dielectric layer 530 maybe deposited by ALD, HDP-CVD, flowable CVD (FCVD) (e.g., a CVD-basedmaterial deposition in a remote plasma system and post curing to make itconvert to another material, such as an oxide), the like, or acombination thereof. In the present embodiment, a planarization process,such as a chemical mechanical polish (CMP), is applied to remove anyexcess first dielectric layer 530, as well as the patterned blanket HM330. After the CMP process is performed, top surfaces of the firstdielectric layer 530 and top surfaces of the first and second fins, 410and 420, are substantially coplanar.

Referring to FIGS. 1 and 9A-9B, the method 100 proceeds to step 118 byrecessing the second fins 420 and depositing a third semiconductormaterial layer 620 over the recessed second fins 420, while a secondpatterned HM 610 covers the NMOS region. The second patterned HM 610 isformed to protect predetermined regions, such as NMOS region. The secondpatterned HM 610 may include silicon nitride, silicon oxynitride,silicon carbide, silicon carbon nitride, the like, or a combinationthereof. The second patterned HM 610 is formed similarly in manyrespects to the first patterned HM 212 discussed above in associationwith FIGS. 5A-5B.

The second fins 420 may be recessed by a selective dry etch, a selectivewet etch, or combination thereof. The etching selectively recesses thesecond fin 420 without substantially etching the first dielectric layer530.

The third semiconductor material layer 620 may include Ge, GaAs, AlGaAs,SiGe, GaAsP, and/or other suitable materials. The third semiconductormaterial layer 620 is formed similarly in many respects to the firstsemiconductor material layer 310 discussed above in association withFIGS. 3A-3B.

Referring to FIGS. 1 and 10A-10B, the method 100 proceeds to step 120 byrecessing the first dielectric layer 530 around the second and thirdsemiconductor material layers, 320 and 620, to laterally expose them. Inthe present embodiment, the etching depth is controlled in the NMOSregion such that the second semiconductor material layer 320 is fullyexposed and the dielectric layer 510 is, at least, partially exposed andin the PMOS the third semiconductor material 620 is fully exposed andsubstrate 210 is, at least, partially exposed. As shown, a top surface530T of the recessed first dielectric layer 530 is below a top surface510T of the semiconductor dielectric material layer 510 in the NMOSregion and below the bottom surface 620B of the third semiconductormaterial layer 620 in the PMOS region.

In some embodiments, the first dielectric layer 530 is recessed by aselective dry etch, a selective wet etch, or combination thereof. Theetching selectively recesses the first dielectric layer 530 withoutsubstantially etching the second and third semiconductor materiallayers, 320 and 620.

For the sake of clarity and to better illustrate the concepts of thepresent disclosure, the exposed second semiconductor material layer 320is referred to as a third fin 630 and the exposed third semiconductormaterial layer 620 is referred to as a fourth fin 640. Thus the thirdfin 630 is formed over and in physical contact with the dielectric layer510 of the first fin 410 and the fourth fin 640 is formed over and inphysical contact with the second fin 420. As discussed above, thedielectric layer 510 provides an electric insulation enhancement for thethird fins 630.

Referring to FIGS. 1 and 11A-11B, the method 100 proceeds to step 122 byforming a first capping layer 650 over the fourth fins 640 to preventout-diffusion. In one embodiment, the first capping layer 650 includesSi to prevent out-diffusion of Ge from the SiGe fin 640 (the fourthfin). In some embodiments, first, the first capping layer 650 isdeposited over the substrate 210 by ALD, CVD, PVD, or other propertechniques. Then a patterned HM is formed to cover the first cappinglayer 650 over the fourth fins 640. The first capping layer is thenetched through the patterned HM. The first capping layer 650 is removedby a selective etch. The patterned HM is removed by another etchingprocess.

Referring to FIGS. 1 and 12A-12B, the method 100 proceeds to step 124 byforming a second capping layer 660 over the third fins 630 and thefourth fins 640. As shown, the second capping layer 660 is disposeddirectly on second semiconductor material layer 320, dielectric layer510, and first dielectric layer 530 in the NMOS region and the secondcapping layer 660 is disposed directly on first capping layer 650,second fins 420, and first dielectric layer 530 in the PMOS region. Thesecond capping layer 660 may include silicon nitride, siliconoxynitride, silicon carbide, silicon carbon nitride, or other propermaterial. In the present embodiment, the second capping layer 660 isdifferent from the first dielectric layer 530 to achieve etchingselectivity during a subsequent etch, which will be described later. Inone embodiment, the second capping layer 660 includes silicon nitride.The second capping layer 660 may be deposited by ALD, CVD, PVD, or otherproper techniques.

Referring to FIGS. 1 and 13A-13B, the method 100 proceeds to step 126 byforming a second dielectric layer 670 over the second capping layer 660.The second dielectric layer 670 is similar in many respects to the firstdielectric layer 530 discussed above in association with FIGS. 8A-8B. Inone embodiment, the second dielectric layer 670 has same material as thefirst dielectric layer 530. During formation of the second dielectriclayer 670, the second capping layer 660 protects the third and fourthfins, 630 and 640 to prevent adverse impacts, such as a furtheroxidation during an anneal process performed after forming the seconddielectric layer 670 by a FCVD process.

In the present embodiment, a planarization process, such as a CMP, isapplied to remove any excess second dielectric layer 670 and planarizetop surface of the second dielectric layer 670 with respect to the topsurface of the third and fourth fins, 630 and 640. In some embodiments,the second capping layer 660 serves as an etching-stop layer in the CMPprocess to improve recessing process window.

Referring to FIGS. 1 and 14A-14B, the method 100 proceeds to step 128 byrecessing the second dielectric layer 670 to lateral expose the secondcapping layer 660 over the third and fourth fins, 630 and 640. Therecessing is controlled such that a top surface 670T of the seconddielectric layer 670 remains a thickness t above the second cappinglayer 660 in fin trenches 430 and 440, respectively. Thus, the recessedfirst dielectric layer 530, the remaining second dielectric layer 670,and second capping layer 660 form isolation features 680 (or referred toas shallow trench isolation (STI) features) between each of the firstfins 410, the second fins 420, the third fins 630 and the fourth fins640. By controlling the remaining thickness t of the second dielectriclayer 670, the method provides process flexibilities and the feasibilityto achieve a targeted thickness of the STI feature 680.

The second dielectric layer 670 may be recessed by a selective dry etch,a selective wet etch, or combination thereof. The etching selectivelyrecesses the second dielectric layer 670 without substantially etchingthe second capping layer 660. Therefore, the second capping layer 660protects the third and fourth fins, 630 and 640 to avoid adverse impactson the third and fourth fins during the recessing process, such as finheight loss.

Referring to FIGS. 1 and 15A-15B, the method 100 proceeds to step 130 byremoving a portion of the second capping layer 660 from the third andfourth fins, 630 and 640. In the present embodiment, the second cappinglayer 660 may be removed by a selective dry etch, a selective wet etch,or combination thereof. The etching selectively removes the secondcapping layer 660 without substantially etching the second dielectriclayer 670, the second semiconductor material layer 320 and the firstcapping layer 650. Therefore, the second capping layer 660 underneaththe second dielectric layer 670 in the fin trenches, 430 and 440,remains intact.

Referring to FIGS. 16A-16B, in some embodiments, the third and fourthfins, 630 and 640, each includes source/drain (S/D) regions 710 and agate region 715. In furtherance of the embodiment, one of the S/Dregions 710 is a source region, and another of the S/D regions 710 is adrain region. The S/D regions 710 are separated by the gate region 715.

Referring again to FIGS. 1 and 16A-16B, the method 100 proceeds to step132 by forming a gate stack 720 and sidewall spacers 730 on sidewalls ofthe gate stack 720 in the gate region 715. In one embodiment using agate-last process, the gate stack 720 is a dummy gate and will bereplaced by the final gate stack at a subsequent stage. Particularly,the dummy gate stacks 720 are to be replaced later by a high-kdielectric layer (HK) and metal gate electrode (MG) after high thermaltemperature processes, such as thermal annealing for source/drainactivation during the sources/drains formation.

The dummy gate stack 720 is formed over the substrate 210, includingwrapping over portions of the third and fourth fins, 630 and 640. In oneembodiment, the dummy gate stack 720 includes an electrode layer 722, asilicon oxide layer 724 and a gate HM 726. The electrode layer 722 mayinclude polycrystalline silicon (polysilicon). The gate HM 726 includesa suitable dielectric material, such as silicon nitride, siliconoxynitride or silicon carbide. The dummy gate stack 720 is formed by asuitable procedure including deposition, lithography patterning andetching. In various examples, the deposition includes CVD, PVD, ALD,thermal oxidation, other suitable techniques, or a combination thereof.The etching process may include dry etching, wet etching, and/or otheretching methods (e.g., reactive ion etching).

The sidewall spacers 730 may include a dielectric material such assilicon oxide, silicon nitride, silicon carbide, silicon oxynitride, orcombinations thereof. The sidewall spacers 730 may include a multiplelayers. Typical formation methods for the sidewall spacers 730 includedepositing a dielectric material over the gate stack 720 and thenanisotropically etching back the dielectric material. The etching backprocess may include a multiple-step etching to gain etch selectivity,flexibility and desired overetch control.

Referring to FIGS. 1 and 17A-17B, the method 100 proceeds to step 134 byforming first S/D features 810 in the S/D regions 710 of the NMOS regionand second S/D feature 812 in the S/D region 710 of the PMOS region. TheS/D features, 810 and 812, may be formed by recessing a portion of thethird and fourth fins, 630 and 640, in the S/D regions 710 to form S/Drecessing trenches and epitaxially growing a fourth and fifthsemiconductor material layers, 815 and 816, in the S/D recessingtrenches. The fourth and fifth semiconductor material layers, 815 and816, may include Ge, Si, GaAs, AlGaAs, SiGe, GaAsP, and/or othersuitable material. The first and second S/D features, 810 and 812, maybe formed by one or more epitaxy or epitaxial (epi) processes. The firstand second S/D features, 810 and 812, may be in-situ doped during theepi process. For example, the epitaxially grown Si epi first S/D feature810 may be doped with carbon to form Si:C S/D features, phosphorous toform Si:P S/D features, or both carbon and phosphorous to form SiCP S/Dfeatures; the epitaxially grown SiGe second S/D features 812 may bedoped with boron. In one embodiment, the first and second S/D features,810 and 812, are not in-situ doped, an implantation process (i.e., ajunction implant process) is performed to dope the first and second S/Dfeatures, 810 and 812.

Referring to FIGS. 1 and 18A-18B, the method 100 proceeds to step 136 byforming an interlayer dielectric (ILD) layer 820 over the substrate 210.The ILD layer 820 includes silicon oxide, silicon oxynitride, low kdielectric material and/or other suitable dielectric materials. The ILDlayer 820 may include a single layer or alternative multiple layers. TheILD layer 820 is formed by a suitable technique, such as CVD, ALD andspin-on (SOG). A CMP process may be performed thereafter to removeexcessive ILD layer 820, as well as the third HM 726 and the pad oxidelayer 724, to planarize the top surface of the semiconductor device 200.

Referring to FIGS. 1 and 19A-19B, the method 100 proceeds to step 140 byreplacing the dummy gate stacks 720 with metal gate stacks (MG) 910. Thedummy gate stacks 720 are first removed to form gate trenches. The dummygate stack 720 may be removed by an etch process (such as selective wetetch and/or selective dry etch) designed to have an adequate etchselectivity with respect to the sidewall spacers 730, the ILD layer 820,the second and third semiconductor material layers, 320 and 630. Theetch process may include one or more etch steps with respectiveetchants. Alternatively, the dummy gate stack 720 may be removed by aseries of processes including photolithography patterning and etchingprocess.

The MG stack 910 is then formed in the gate trenches, including wrappingover the third fins 630 and the fourth fins 640. The MG stack 910 mayinclude gate dielectric layer and gate electrode over the gatedielectric. In one embodiment, the gate dielectric layer includes adielectric material layer having a high dielectric constant (HKdielectric layer-greater than that of the thermal silicon oxide in thepresent embodiment) and the gate electrode includes metal, metal alloyor metal silicide. The formation of the MG stack 910 may includedepositions to form various gate materials and a CMP process to removethe excessive gate materials and planarize the top surface of thesemiconductor device 200.

The semiconductor device 200 is further illustrated in FIGS. 20A and20B, in a sectional fragmental view. Particularly, a portion of thesemiconductor device 200 is zoomed in for clarity. In embodiment, thegate dielectric layer 914 includes an interfacial layer (IL) and a HKdielectric layer. The IL includes oxide, HfSiO and oxynitride, depositedby a suitable method, such as ALD, CVD, thermal oxidation or ozoneoxidation. The HK dielectric layer is deposited on the IL by a suitabletechnique, such as ALD, CVD, metal-organic CVD (MOCVD), physical vapordeposition (PVD), other suitable technique, or a combination thereof.The HK dielectric layer may include LaO, AlO, ZrO, TiO, Ta₂O₅, Y₂O₃,SrTiO₃ (STO), BaTiO₃ (BTO), BaZrO, HfZrO, HfLaO, HfSiO, LaSiO, AlSiO,HfTaO, HfTiO, (Ba,Sr)TiO₃ (BST), Al₂O₃, Si₃N₄, oxynitrides (SiON), orother suitable materials.

A metal gate (MG) electrode 916 may include a single layer oralternatively a multi-layer structure, such as various combinations of ametal layer with a work function to enhance the device performance (workfunction metal layer), liner layer, wetting layer, adhesion layer and aconductive layer of metal, metal alloy or metal silicide). The MGelectrode 916 may include Ti, Ag, Al, TiAlN, TaC, TaCN, TaSiN, Mn, Zr,TiN, TaN, Ru, Mo, Al, WN, Cu, W, any suitable materials or a combinationthereof. The MG electrode 916 may be formed by ALD, PVD, CVD, or othersuitable process. The MG electrode 916 may be formed separately for theNMOS and PMOS with different metal layers. A CMP process may beperformed to remove excessive MG electrode 916.

Referring again to FIGS. 19A and 20A, in the NMOS region, the third fin630 is formed by the second semiconductor material layer 320 in the gateregion 715. The third fin 630 is disposed over and in physical contactwith the dielectric layer 510. The lower portion of the first fins 410includes a portion of the substrate 210. The third fin 630 is wrapped bythe MG stack 910. The STI feature 680 is formed between each of twofirst fins 410. The STI feature 680 includes the first dielectric layer530, the second capping layer 660 disposed over and in physical contactwith the first dielectric layer 530 and the second dielectric layer 670disposed over and in physical contact with the second capping layer 660.The second dielectric layer 670 has thickness t. The top surface 530T ofthe first dielectric layer 530 is below the top surface 510T of thedielectric layer 510.

Referring again to FIGS. 19B and 20B, in the PMOS region, fourth fin 640is formed by the third semiconductor material layer 620 in the gateregion 715. The fourth fin 640 is deposited over and in physical contactwith the second fin 420, which includes a portion of the substrate 210.The fourth fin 640 is wrapped by the MG stack 910. The STI feature 680is formed between each of two second fins 420. The STI feature 680includes the first dielectric layer 530, the second capping layer 660deposited over and in physical contact with the first dielectric layer530 and the second dielectric layer 670 deposited over and in physicalcontact with the second capping layer 660. The second dielectric layer670 has thickness t. The top surface 530T of the first dielectric layer530 is below the bottom surface 620B of the dielectric layer 510.

The semiconductor device 200 may undergo further CMOS or MOS technologyprocessing to form various features and regions known in the art. Forexample, subsequent processing may form various contacts/vias/lines andmultilayers interconnect features (e.g., metal layers and interlayerdielectrics) on the substrate 210, configured to connect the variousfeatures to form a functional circuit that includes one or more FinFETs.In furtherance of the example, a multilayer interconnection includesvertical interconnects, such as vias or contacts, and horizontalinterconnects, such as metal lines. The various interconnection featuresmay implement various conductive materials including copper, tungsten,and/or silicide. In one example, a damascene and/or dual damasceneprocess is used to form a copper related multilayer interconnectionstructure.

Additional steps may be implemented before, during, and after the method100, and some steps described above may be replaced or eliminated forother embodiments of the method.

As an example, in one embodiment, steps of 104, 106, 108 and 114, forforming the dielectric layer 510, are eliminated. Thus, in the NMOSregion, fifth fins 950 are formed including a portion of the substrate210, as shown in FIG. 21A. The fifth fin 950 is wrapped by the MG stack910. The STI feature 680 is formed between each of two fifth fins 950.The STI feature 680 includes the first dielectric layer 530, the secondcapping layer 660 deposited over and in physical contact with the firstdielectric layer 530 and the second dielectric layer 670 deposited overand in physical contact with the second capping layer 660. The seconddielectric layer 670 has thickness t.

Based on the above, the present disclosure offers a method forfabricating a semiconductor device. The method employs a capping layerto prevent adverse impacts on fin structures during forming isolationregions between fin structures. The method also employs forming adielectric layer over the capping layer to achieve a targeted thicknessof the isolation region. The method provides a quite simple and flexibleprocess flow for formations of fin structures and isolation region. Themethod demonstrates device performance and reliability improvements.

Thus, the present disclosure provides one embodiment of a methodfabricating a semiconductor structure. The method includes forming afirst fin structure and a second fin structure over a substrate, whichhas a first trench positioned between the first and second finstructures. The method also includes forming a first dielectric layerwithin the first trench, recessing the first dielectric layer to exposea portion of the first fin structure, forming a first capping layer overthe exposed portion of the first fin structure and the recessed firstdielectric layer in the first trench, forming a second dielectric layerover the first capping layer in the first trench while the first cappinglayer covers the exposed portion of the first fin feature and removingthe first capping layer from the first fin structure.

The present disclosure also provides another embodiment of a methodfabricating a semiconductor structure. The method includes providing asubstrate having a first region and a second region, forming a first finstructure and a second fin structure in the first region, which has afirst trench positioned between the first and second fin structures. Themethod also includes forming a third fin structure and a fourth finstructure in the second region, which has a second trench positionedbetween the third and fourth fin structures. The third fin structure hasa different material than the first fin structure. The method alsoincludes forming a first dielectric layer in the first and secondtrenches, recessing the first dielectric layer in the first trench toexpose a portion of the first and second fin structures and recessingthe first dielectric layer in the second trench to expose a portion ofthe third and fourth fin structures. The method also includes forming afirst capping layer over the third and fourth fin structures, forming asecond capping layer over the first structure, the second finstructures, the first capping layer, the first and second trenches. Themethod also includes forming a second dielectric layer over the secondcapping layer in the first and second trenches; and removing the secondcapping layer from the first fin structure, the second fin structure andthe first capping layer.

The present disclosure also provides a structure of a device. The deviceincludes a first fin structure in a first region of the substrate, whicha first portion of the substrate, a dielectric layer deposited over andin physical contact with the first portion of the substrate, a firstsemiconductor material layer deposited over and in physical contact withthe dielectric layer. The device also includes a second fin structure ina second region of the substrate, which has a second portion of thesubstrate, a second semiconductor material layer disposed over and inphysical contact with the second portion of the substrate and a firstcapping layer wrapping over the second semiconductor material layer. Thedevice also includes a first isolation structure disposed in thesubstrate adjacent the first fin structure, which has a first dielectriclayer, a second capping layer disposed over and in physical contact withthe first dielectric layer, the second capping layer physicallycontacting the dielectric layer and a second dielectric layer disposedover and in physical contact with the second capping layer. The devicealso includes a second isolation structure disposed in the substrateadjacent the second fin structure, which has the first dielectric layer,the second capping layer disposed over and in physical contact with thefirst dielectric layer, the second capping layer physically contactingthe first capping layer and the second dielectric layer disposed overand in physical contact with the second capping layer. The device alsoincludes a first metal gate wrapping over a portion of the first finstructure and a second metal gate wrapping over a portion of the secondfin structure.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. A method, comprising: forming a first fin structure and a second finstructure over a substrate, wherein a first trench is position betweenthe first and second fin structures; forming a first dielectric layerwithin the first trench; recessing the first dielectric layer to exposea portion of the first fin structure; forming a first capping layer overthe exposed portion of the first fin structure and the recessed firstdielectric layer in the first trench, wherein a portion of the firstcapping layer extends from the first fin structure to the second finstructure; forming a second dielectric layer over the first cappinglayer in the first trench while the first capping layer covers theexposed portion of the first fin structure and the portion of the firstcapping layer extends from the first fin structure to the second finstructure; and removing the first capping layer from the first finstructure.
 2. The method of claim 1, wherein forming the first finstructure and the second fin structure over the substrate, includes:epitaxially growing a first semiconductor material layer over thesubstrate; epitaxially growing a second semiconductor material layer ontop of the first semiconductor material layer; etching the second andfirst semiconductor material layers to form the first fin structure, thesecond fin structure and the first trenches; and converting the firstsemiconductor material layer to a dielectric layer.
 3. The method ofclaim 1, wherein forming the first fin structure and the second finstructure over the substrate, includes: forming a patterned mask overthe substrate; and removing a portion of the substrate through thepatterned mask to form first and second fin structures and the firsttrenches.
 4. The method of claim 2, wherein the first dielectric layeris recessed to fully expose the second semiconductor material layer andpartially expose the dielectric layer.
 5. The method of claim 1, whereinforming the second dielectric layer over the first capping layer in thetrench while the first capping layer covers the exposed portion of thefirst fin feature, includes: depositing the second dielectric layer overthe first capping layer over the first trench, the first fin structuresand the second fin structure; and recessing the second dielectric layerby a selective etch process, which recesses the second dielectric layerbut does not substantially etch the first capping layer.
 6. The methodof claim 1, further comprising: forming a third fin structure and afourth fin structure over the substrate, wherein a second trench isposition between the third and fourth fin structures, wherein the secondtrench is filled with recessed first dielectric layer; forming a fincapping layer over the third fin structure; forming the first cappinglayer over the fin capping layer and the recessed first dielectric layerin the second trench; forming the second dielectric layer over the firstcapping layer in the second trench while the first capping layer coversthird fin structure; and removing the first capping layer.
 7. The methodof claim 6, wherein forming the third fin structure and the fourth finstructure over the substrate includes: etching the substrate to form afin feature and the second trench; filling in the second trench with thefirst dielectric layer; removing a portion the fin feature to form a fintrench; epitaxially growing a third semiconductor material layer in thefin trench; and recessing the firs dielectric layer to fully exposed thethird semiconductor material layer.
 8. The method of claim 1, furthercomprising: after removing the first capping layer, forming dummy gatesin a gate region in the first fin structure; forming a source/drain(S/D) features in a S/D region in the first fin structure; and replacingthe dummy gates with a high-k/metal gate (HK/MG) wrapping over the firstfin structure.
 9. A method, comprising: providing a substrate having afirst region and a second region; forming a first fin structure and asecond fin structure in the first region, wherein a first trench isposition between the first and second fin structures; forming a thirdfin structure and a fourth fin structure in the second region, wherein asecond trench is position between the third and fourth fin structures,wherein the third fin structure has a different material than the firstfin structure; forming a first dielectric layer in the first and secondtrenches; recessing the first dielectric layer in the first trench toexpose a portion of the first and second fin structures and recessingthe first dielectric layer in the second trench to expose a portion ofthe third and fourth fin structures; forming a first capping layer overthe third and fourth fin structures; forming a second capping layer overthe first structure, the second fin structure, the first capping layer,the first and second trenches; forming a second dielectric layer overthe second capping layer in the first and second trenches; and removingthe second capping layer from the first fin structure, the second finstructure and the first capping layer.
 10. The method of claim 9,wherein forming the first fin structure and the second fin structure inthe first region includes: epitaxially growing a first semiconductormaterial layer over the substrate; epitaxially growing the secondsemiconductor material layer on top of the first semiconductor materiallayer; and etching the second and first semiconductor material layers toform the first fin structure, the second fin structure and the firsttrenches; and converting the first semiconductor material layer to thedielectric layer.
 11. The method of claim 10, wherein recessing thefirst dielectric layer in the first trench to expose the portion of thefirst and second fin includes recessing the first dielectric layer tofully expose the second semiconductor material layer and partial of thedielectric layer.
 12. The method of claim 9, wherein forming the firstfin structure and the second fin structure in the first region includes:forming a patterned mask over the substrate; and removing a portion ofthe substrate through the patterned mask to form first fin structure,the second fin structure and the first trenches.
 13. The method of claim9, wherein forming the third fin structure and the fourth fin structurein the second region, includes: etching the substrate to form a finfeature and the second trench; filling in the second trench with thefirst dielectric layer; removing a portion the fin feature to form a fintrench; epitaxially growing a third semiconductor material layer in thefin trench; and recessing the firs dielectric layer to fully exposed thethird semiconductor material layer.
 14. The method of claim 13, whereinrecessing the first dielectric layer in the second trench to expose theportion of the third and fourth fin includes recessing the firstdielectric layer to fully expose the third semiconductor material layer.15. The method of claim 9, wherein forming the first capping layer overthe third fin structure and the fourth fin structure in the secondregion, includes: depositing the first capping layer over the first,second, third and fourth fin structures; covering the third finstructure and fourth fin structure with a hard mask; and removing thefirst capping layer from the first and second fin structures.
 16. Themethod of claim 9, wherein forming the second dielectric layer over thesecond capping layer in the first and second trenches includes:depositing the second dielectric layer over the substrate, includingover the first fin structure, the second fin structure, the secondcapping layer in both of the third and fourth fin structure, the firsttrench and second trenches; and removing the second dielectric layerfrom the first fin structure, the second fin structure, the secondcapping layer in both of the third and fourth fin structure.
 17. Themethod of claim 16, wherein the second dielectric layer is removed by aselective etch process which recesses the second dielectric layer butdoes not substantially etch the second capping layer.
 18. The method ofclaim 9, further comprising: after removing the second capping layerfrom the first and second fin structures, forming dummy gates in gateregions over the first fin structure, the second fin structure, thethird fin structure and the fourth fin structure; forming a source/drain(S/D) features in S/D regions over the first fin structure, the secondfin structure, the third fin structure and the fourth fin structure; andreplacing the dummy gates with a high-k/metal gate (HK/MG). 19-20.(canceled)
 21. A method comprising: forming a first fin structure over asubstrate; forming a second fin structure over the substrate, whereinthe second fin structure is formed of a different material than thefirst fin structure; forming a first capping layer over the second finstructure; forming a second capping layer over the first fin structureand the first capping layer over the second fin structure, wherein thesecond capping layer is formed of a different material than the firstcapping layer; forming a dielectric layer over the second capping layer;recessing the dielectric layer to expose a portion of the second cappinglayer; and removing the exposed second capping layer such that the firstfin structure is exposed and the second fin structure is covered by thefirst capping layer.
 22. The method of claim 21, wherein the second finstructure includes germanium, wherein the first capping layer includessilicon; and wherein the second capping layer includes silicon nitride.